Radio receiving system



P 1936- B. D. H. TELLEGEN 2,054,528

RADIO RECEIVING SYSTEM Filed July 17, 1934 INVENTOR 5EEM4EDMSQ Easels-W ATTORNEY Patented Sept. 15, 1936 NETED STATES 2,054,528 RADIO RECEIVING SYSTEM Application July 17, 1934, Serial No. 735,571 In the Netherlands July 20, 1933 3. Claims. 7 (01. 250-40) This invention relates to circuit arrangements for readjusting tuned circuits. More particularly, it relates to arrangements for obtaining the minimum-capacity adjustment of a tuned circuit which is adapted to be used either for long wave reception or short wave reception.

If a receiving set comprises a plurality of tuned circuits all of which are simultaneously tuned by a single manipulation, the circuits must be so calibrated that the variation of the frequency to which the circuits are tuned as a function of the position of the tuning condensers, is equal for all circuits.

In order to ensure an absolutely equal" variation of the frequency the circuits are readjusted at the minimum-capacity position or" the tuning condensers by means of adjusting condensers, which are known as trimmers. In this manner the minim ii-capacity is equalized for all circuits.

It is customary to construct the circuits in such a manner that they are adapted for receiving a plurality of ranges of wave lengths. Since for the reception of long waves the self induction present in the circuit must be larger with a given capacity than for the reception of short waves the coil or" the circuit is often constructed in such a manner that one or more parts thereof can be short circuited.

In the drawing, Figs. 1 and 2 are respectively two-band and three-band tunable circuits serving to explain the invention. Figs. 3 and 4 are alternative arrangements of two-band tunable circuits in accordance with the present invention, and Figs. 5 and 6 are alternative arrangements of three-band tunable circuits in accordance with the present invention.

With the usual circuit arrangements the trimmers are preferably connected in parallel with the tuning condenser and in parallel with the part or parts of the coil which are short-circuited for receiving the short wave ranges, in the manner indicated in Figures 1 and 2 wherein C denotes the tuning condenser, L the inductance coil and C1, C2 and C3 the trimmers.

The circuit represented in Figure 1 can be adjusted for the reception of two wave ranges. If the switch K is closed, the part b of the coil L is short-circuited and the circuit can be tuned to high frequencies. The minimum capacity is readjusted by means of the trimmer C1. For the reception of long waves the switch K is opened. In this case the minimum-capacity is readjusted with the aid 01" the trimmer C2. Since the minimum-capacity of the circuit is determined by the minimum capacity of the tuning condenser C and the capacity to which the trimmers C1 and C2 are adjusted, one will be bound to'a comparatively large minimum-capacity, so that tuning below a definite wave-length is not possible. With the usual receiving sets, for instance, it will not be possible to tune below meters for the long wave range. In order to avoid this drawback and to increase the wave range to which the circuit can be adjusted, the minimum-capacity of the circuit must be reduced. Accordingly, the trimmer C1 connected in parallel with the tuning condenser (Figs. 1 and 2) is replaced by a trimmer C4 connected in parallel with the coil part which is not short circuited for the reception of short waves (Fig. 4).

For receiving short waves with such an arrangement the minimum-capacity is adjusted by means of the trimmer C4, the trimmer C2 being used to adjust the minimum-capacity of the circuit for the reception of long waves. Since with the reception of long waves C4 is parallel with a small part of the self induction of the circuit, the resulting minimum-capacity will be much smaller than when the trimmers are connected in parallel with the tuning condenser and with the part b of the coil L as in the circuit of Fig. 1. In this manner it is possible to tune to shorter waves in the long wave range than it was hitherto possible.

For the long wave range the same result can be obtained by replacing the trimmer C2 connected in parallel with the part b of the coil L by a trimmer C4 connected in parallel with the part a (Fig. 3). With this arrangement the minimumcapacity of the circuit when adjusting to the reception oi short waves will be larger than with the arrangements represented in Figures 1 and 4. Practically, however, this drawback is of little importance, since it is possible with short waves to adjust to sufficiently low wave lengths.

If the circuit can be tuned to the reception of more than two wave ranges, according to Fig. 2, a range which is as large as possible is likewise ensured for each wave range by making the minimum capacity of the circuit as small as possible when adjusting to the reception of the different wave ranges.

For this purpose the trimmers, according to the invention, are not connected in the manner hitherto used, as indicated in Fig. 2, but in such a manner that they are in parallel with the parts a, b and c of the coil L. This is shown in Fig. 6 wherein the trimmer condensers C4, C5 and Cs shunt the coil portions a, b and 0, respectively, of

the coil L. It is also possible to increase the minimum-capacity of the circuit for the long wave ranges by means of the circuit arrangement represented in Fig. 5. With this arrangement as well as with that shown in Fig. 3, the minimum-capacity of the circuit will be increased when adjusting to'the reception of short waves.

It will be appreciated that it is also possible to connect a trimmer in parallel with the part b instead of with the part c of the coil.

If the circuit is so constructed that it can be tuned to more than three ranges of wave lengths then there is a larger number of possibilities to make the minimum-capacity as small as possible when adjusting to the reception of long wave ranges. After the foregoing it is perfectly clear in what manner the trimmers must be provided in this case.

What-I claim is:

1. A multi-range tunable circuit comprising a tapped inductance, a variable condenser, and a trimmer condenser connected in shunt to each tapped portion of the inductance, said trimmer condensers being connected serially and across the entire inductance, and means for alternatively short-circuiting one or more of said tapped portions and the corresponding trimmer condensers associated with said tapped portions.

2. A tunable circuit comprising an inductance and a variable condenser capable of tuning the circuit through a' certain wave-length range, means for short-circuiting a major portion of the inductance to enable the circuit to be tuned through a shorter and substantially different wave-length range, a trimmer condenser connected across the major portion of the inductance, and a second trimmer condenser in series with the first connected across the remaining portion of the inductance.

3. A tunable circuit comprising an inductance and a variable condenser, means for short-circuiting portions of the inductance to enable the circuit to be tuned to difierent wave-lengths, a plurality of trimmer condensers, equal to the number of wave-length ranges to which thecircuit is capable of being tuned, serially connected between the terminals of the inductance, each trimmer condenser being connected in shunt to a different portion of the inductance.

BERNARDUS D. H. TELLEGEN. 

